1. Field of the Invention
The present invention relates to an electromagnetic retarder with a built-in exciter, and more specifically to an electromagnetic retarder with a built-in exciter having such a construction that an eddy-current cylinder for generating braking torque by eddy current is formed by laminating a magnetic material, and an exciter core divided into a plurality of segments is used as the exciter.
2. Description of the Prior Art
FIG. 19 is a longitudinal sectional diagram illustrating the essential part of an electromagnetic retarder with a built-in exciter of a conventional type, viewed in the direction of arrows AOB of FIG. 20. FIG. 20 is a right-hand side view of FIG. 19.
In FIGS. 19 and 20, a support disc 1 that is of a dish- or cup-shape on both sides thereof is rotatably provided between a flange 2-1 on the side of the output-shaft of a transmission 2 and a flange 3-1 on the side of a propeller-shaft 3, as shown in FIG. 19. The support disc 1 is formed into a shape of an open-ended dish or cup by flange members on both sides of the rim thereof, and coaxially fitted between the flange 2-1 on the side of the output shaft and the flange 3-1 on the side of the propeller shaft 3 with bolts 4 and nuts 5.
An eddy-current cylinder 7 is disposed coaxially with the support disc 1 via a mounting disc 6 outside the support disc 1. The eddy-current cylinder 7 is made of an iron material. In some cases, the mounting disc 6 may be formed integrally with the eddy-current cylinder 7.
A cylindrical support member 8 made of a magnetic material is disposed in a space formed by the outside of the support disc 1 having on both side thereof members formed into an open-end disc or cup shape, and the eddy-current cylinder 7. One end of the cylindrical support member 8 is fixedly fitted to a support plate 9 having a recess at the center thereof. The support plate 9 is fixedly fitted to an end of the transmission 2 with bolts 10. In this case, too, the support plate 9 may be formed integrally with the support member 8.
A pole core 11 made of a magnetic material is fitted with bolts 12 to the outer circumferential surface of the cylindrical support member 8 disposed in a space formed by the outside of the support disc 1 having on both side thereof members formed into an open-end disc or cup shape, and the eddy-current cylinder 7. An air gap is formed between the pole core 11 and the inner circumferential surface of the eddy-current cylinder 7. A field coil 13 is wound on the pole core 11. An exciter core 14 is fixedly fitted to the inner circumferential surface of the support member 8, and an exciter coil 15 is wound on a slot provided on the exciter core 14.
On the outer circumferential surface of the support disc 1 having on both sides thereof members formed into an open-end dish- or cup-shape, provided at equal intervals are permanent magnets 16 formed into an arc-segment shape, for example, arranged in alternately different polarities. An air gap is formed between the permanent magnet 16 and the exciter core 14. The exciter coil 15 wound on the exciter cores 14 and the permanent magnets 16 constitute an exciter.
The a-c voltage generated in the exciter coil 15 is rectified by rectifying means, and a field current flows in the field coil 13 by turning on a retarder main switch.
Numeral 17 refers to a heat shield plate for shielding the radiant heat from the eddy-current cylinder 7 caused by the heat as an eddy-current loss to inhibit temperature rise in the field coil 13. Numeral 18 refers to a radiating fin for dissipating the heat generated in the eddy-current cylinder 7 as an eddy-current loss into the atmosphere.
The operation of the conventional type of the retarder with a built-in exciter having the aforementioned construction will be described in the following.
As the output shaft, that is, the flange 2-1 on the side of the output shaft of the transmission 2 is rotated, the support disc 1, the permanent magnet 16, the mounting disc 6 and the eddy-current cylinder 7 are also rotated en bloc. At this time, the rotation is also transmitted to the flange 3-1 on the side of the propeller shaft 3.
By turning on the retarder main switch to activate the retarder, a d-c voltage obtained by rectifying the a-c voltage generated in the exciter coil 15 is applied to the field coil 13 to cause a field current to flow. As a result, the pole core 11 is magnetized to N and S poles alternately, and an eddy current is produced in the eddy-current cylinder 7. A braking torque is generated in the direction opposite to the rotation of the eddy-current cylinder 7 between the eddy current and the field formed by the pole core 11, applying a braking action to the rotation of the flange 2-1 on the side of the output shaft.
FIG. 21 is a front view of the eddy-current cylinder of the conventional type in which the mounting disc and the eddy-current cylinder are formed integrally, FIG. 22 is a partial cross-sectional view of the side part of FIG. 21. In the figures, the eddy-current cylinder 39 is made of a magnetic material, such as iron, has inclined radiating fins 40 on the outer circumferential surface thereof, and is equivalent to the mounting disc 6 and the eddy-current cylinder 7 described in FIGS. 19 and 20. The outside and inside diameters of the eddy-current cylinder 39 are Lo and Lr, respectively, and the thickness of the core (equal to the thickness of the eddy-current cylinder 7 in FIG. 19) is t2, as shown in FIG. 22.
However, the fins of the eddy-current cylinder 7 and the eddy-current cylinder 39, the radiating fin 18, and the inclined radiating fin 40 shown in FIGS. 21 and 22 as used in the electromagnetic retarder with a built-in exciter of the conventional type shown in FIGS. 19 and 20 have been machined with a gear hobbing machine after machined with a lathe.
The conventional manufacturing method for manufacturing the eddy-current cylinders 7 and 39 having the radiating fins 18 and the inclined radiating fins 40 has had low manufacturing yield, and involved long hours for machining the radiating fins 18 and the inclined radiating fins 40, leading to increased manufacturing cost.
Furthermore, the conventional type of the electromagnetic retarder with a built-in exciter requires splash-proof specifications to prevent water splashes during the travel of a truck from falling on the retarder, lowering the insulation of the exciter. Although there can be a method of covering the exciter coil and other parts with resin, etc. after assembly with the conventional type of the electromagnetic retarder with a built-in exciter, this method could lead to lowered productivity. To cope with this, a method of dividing the exciter core into sections, providing water-proofing measures to each section and assembling the water-proofed sections into one piece has been proposed. This method also has the risk of increasing magnetic resistance, adversely affecting the performance.
It is an object of the present invention to provide an eddy-current cylinder for electromagnetic retarders having such a construction that braking torque characteristics are improved and the manufacture of eddy-current cylinders is made easy, thereby manufacturing cost is reduced, by producing a core by laminating a magnetic material, and providing short-circuiting means allowing eddy current to flow therein in the axial direction of the eddy-current cylinder.
It is another object of the present invention to provide an exciter for electromagnetic retarders having such a construction that water proofness is imparted to the exciter coil of the retarder, and an exciter core is divided into a plurality of pieces to facilitate the assembling of the retarder with a built-in exciter while preventing the exciter performance from deteriorating due to the division of the exciter core.
It is a further object of the present invention to provide an electromagnetic retarder with a built-in exciter having the aforementioned eddy-current cylinder and exciter for the retarder.
In disclosed embodiments, the eddy-current cylinder comprises a core formed by laminating a magnetic material, and short-circuiting means provided in the laminated core in the axial direction of the cylinder for allowing the generated eddy current to flow therein. The retarder exciter comprises an exciter coil wound on bobbins disposed on the outside thereof facing a plurality of permanent magnets via an air gap, cylindrical exciter cores molded by a molding material together with the bobbins and the exciter coil, cylindrical pole cores provided integrally with the exciter cores on the outer periphery of the exciter cores and having field coils and a plurality of magnetic poles alternately magnetized to N and S poles by a field current caused to flow in the field coils by a voltage generated in the exciter coil, and an eddy-current cylinder provided outside the pole cores facing the pole-core magnetic poles via an air gap; the cylindrical exciter cores molded by a molding material together with the bobbins and the exciter coil being divided into a plurality of pieces to form molded exciter cores; the molded shape of both ends of the divided molded exciter core pieces is such that the overhanging part of the molding material above the bobbins is tapered toward the ends of the molder exciter core with respect to the inside diameter surface of the molded exciter core, with the corner part thereof at both ends being chamfered and the amount of overhand being gradually decreased; the end faces at both ends of each of the divided molded exciter core pieces being formed in such a state that the exciter core surface protrudes from the molded surface; the molded shape of the groove width portion at the exciter coil insertion hole of the bobbin of the molded exciter core has such a construction that the overhang portion of the molding material above the bobbin is tapered toward the center of said groove width with respect to the inside diameter surface of the molded exciter core; with the amount of overhang being gradually decreased; both ends of said exciter coil wound on said molded exciter core are drawn through holes on a collar, of a shouldered embedded construction, mounted on a collar mount protruding from the outer circumferential surface of said molded exciter core in the axial direction; areas around the embedded part of said collar being molded by a molding material.